1. Field of the Invention
The invention relates to non-destructive ultrasonic testing of tubular goods for detection of small internal cracks and other types of discontinuities or imperfections. More specifically, the instant invention relates to apparatus for conducting the inspection of tubular goods employed in the drilling of oil and gas wells, while such tubular goods are being passed out of or into the well borehole during a drilling operation, to provide on-site inspection of the drill pipe employed in the drilling operation or well casing or tubing while it is being set.
2. Description of the Prior Art
The use of ultrasonic testing techniques, and specifically of ultrasonic crystals, for detecting discontinuities in metal products is a common mode of nondestructive testing. The crystals employed are typically piezoelectric crystals made of a material such as quartz. These crystals produce ultrasonic vibrations in response to a voltage or appropriate frequency impressed upon the crystal. When inspecting a tubular product for internal flaws using a reflection method, the crystal is maintained in a position relative to the surface of the product to transmit a short duration sonic wave pulse into the product at an angle such that a defect or discontinuity will cause the waves to be reflected to the crystal and produce a voltage response in the crystal. Since the crystal is de-energized immediately following the pulsed emission of a wave, reflected waves are received during de-energized periods and hence the reflected waves will produce a discernible signal which may be monitored, for example, on a cathode ray tube or a strip chart recorder. Pulse repetition rates of between 60 and 2000 pulses per second are employed for various types of inspections.
Typically, an ultrasonic inspection device will be calibrated using a standard identical to the goods being inspected. The standard may have one or more discontinuities of known magnitude so that the response of the device to known imperfections may be ascertained, and standards for accepting or rejecting the inspected goods may be established.
Ultrasonic inspection techniques are most typically employed at the site of manufacture of the articles being inspected. Thus, plate or tubular goods are typically inspected at the manufacturing plant using techniques which are well-known in the art. However, the on-site inspection of tubular goods presents different and unique problems.
In well drilling operations, drill pipe failure can be a costly and time-consuming occurrence. Washouts or drill string breakage can occur frequently if drill pipe with sufficiently serious imperfections is employed. Most frequently such failures result from internal flaws in the tubular goods being used. Confronted with such a failure, it becomes necessary to trip the pipe out of the borehole to replace the failed joint. In the case of drill string breakage, it is also necessary to fish the parted portion of the string from the borehole before drilling can be recommenced. Hence, the value of an efficacious method of inspection, particularly for internal flaws in drill pipe is obvious.
During drilling operations, the drill string is frequently tripped into and out of the borehole to replace a worn drill bit, to set casing at various levels or to conduct other operations. During these trips, it is preferred to stack the drill pipe vertically within the well derrick rather than transporting it from the elevated rig floor to racks maintained at ground level. In offshore drilling operations, it is also common to stack drill pipe vertically. Inspection of a drilling string is desirably conducted periodically, e.g., every two or three months, to detect the existence of flaws in drill pipe which would render the pipe susceptible to failure in subsequent drilling operations. Hence, to provide most efficient inspection of tubular goods in well drilling operations, it is necessary to provide an inspection device which can inspect tubular goods in a vertical portion in the well derrick. With such a device inspections could be conducted during a tripping operation made necessary by factors such as a replacement of a worn drill bit. Furthermore, since it is necessary to join individual stands of pipe (comprising typically two or three pipe joints or sections) at the rig floor level when assembling a drilling string, it is necessary that a useful inspection device be readily engaged and disengaged from about the pipe being inspected.
U.S. Pat. No. 4,020,688 discloses an effective non-destructive ultrasonic testing apparatus for inspecting tubular goods employed in the drilling of oil and gas wells as such goods are being tripped into or out of the well borehole during a drilling operation. However, this apparatus required that the transducer orientation within the wheel-like search units be readjusted for any change in the size of the tubular member being inspected. Copending U.S. application Ser. No. 620,747, discloses a similar apparatus wherein the electro-acoustic transducers are mounted on a frame by a linkage which maintains the angular relation between the transducer and the tubular member constant regardless of the size of the member being inspected. Although this apparatus overcomes the need to readjust the orientation of the transducers within the search units, it has itself produced an additional problem in that the force with which the search units are urged against the tubular members varies with the diameter of the tubular member.
Thus, there is a need for an ultrasonic testing apparatus for tubular goods which automatically readjusts the orientation of the transducers and maintains a constant force between the search units and the tubular member regardless of the diameter of the tubular member.